Images Are Case-Sensitive
While it makes sense that being a file name it's case-sensitive in some systems, the sensitivity is inconsistent. Particularly, when the case of the attachment (on the Image page itself) does not match the case of the title of the Image page itself, the page is successfully created (this is correct behavior).
However, in this case, when using the IMAGE BB-Code in other posts, the image cannot be loaded because the attachment ID can't be found - the cases in the database look-ups don't match. This problem only presents in vBulletin 4.
Fixed for the next build. Rather than searching the database for the precise attachment, all the attachments in the Image page are returned. If there is more than 1 image, they are matched case-insensitive against the page title to find the right one.